In the employment of a fluid-pressure-responsive control device employing a diaphragm to sense pressure changes, it is common practice to place the peripheral bead of the diaphragm between two cylinder members that have radial flanges at their confronting ends and to tighten the two flanges together by means of numerous screws or bolts to compress the peripheral bead of the diaphragm. One disadvantage of such a construction is the relatively large expense in the machining required to fabricate the parts and to install and tighten the numerous screw fasteners. Another disadvantage is that the construction cannot be relied upon to be leak free over a long service life.
The need for improvement is this regard is especially apparent in the construction of valve actuators that are now increasingly employed for the automatic control of drip irrigation systems. In a drip irrigation system, water is released at ground level at a trickle rate through orifices that are exceedingly small in diameter, the diameter of such an orifice being commonly as small as 0.0058 inch. For such a system to operate in a trouble-free manner, it is mandatory to use large filters to remove foreign particles and clogging materials such as algaes from the water supply. A granular filter bed in a large filter tank used for this purpose becomes progressively clogged with foreign matter and must be periodically back-washed. It is common practice to use an automatic system which carries out a back-wash cycle whenever the pressure drop across the filter bed rises to a predetermined magnitude. A 3-way valve is employed for this purpose which normally directs the water supply in one direction through the filter bed but which, when required, operates to permit reverse flow through the filter bed for a short period of time, to agitate the filter bed and flush away the accumulated debris.
The present invention is directed to the problem of fabricating an actuator for such a 3-way valve wherein a diaphragm responsive to changes in pressure in a control chamber is operatively connected to a valve member that is movable between two limit positions.